我有一个html表单用于更新mysql数据库中的值。在页面加载时，使用数据库中的现有数据填充表。当我发出post命令时，数据库中的所有字段都会更新，除了date。我做错什么了？
mysql表：

----------------------------------------------------------------------------------
|# | Name       | Type         | Collation       | Null | Default     | Extra    |
----------------------------------------------------------------------------------
|1 | ID         | int(11)      |                 | No   | none        | auto_inc |
|2 | username   | varchar(50)  | utf8_general_ci | No   | none        |          |
|3 | date       | date         |                 | No   | none        |          |
|4 | mission    | varchar(100) | utf8_general_ci | No   | none        |          |
|5 | transFrom  | varchar(100) | utf8_general_ci | No   | none        |          |
|6 | transpTo   | varchar(100) | utf8_general_ci | No   | none        |          |
|7 | payment    | varchar(100) | utf8_general_ci | No   | none        |          |
|8 | comment    | text         | utf8_general_ci | No   | none        |          |
|9 | created_at | datetime     |                 | Yes  | curnt_tstmp |          |
----------------------------------------------------------------------------------

形式：

<?php
 require_once("db.php");
 $arr = $conn->getMissionsId();
 $mission_id = isset($_GET['id']) ?  $_GET['id'] : '';

for($i=0; $i < count($arr); $i++) {
  if ($id = $mission_id && $arr[$i]['username'] == $_SESSION['username']) {
      $username = $arr[$i]['username'];
      $date = $arr[$i]['date'];
      $mission = $arr[$i]['mission'];
      $from = $arr[$i]['transpFrom'];
      $to = $arr[$i]['transpTo'];
      $payment = $arr[$i]['payment'];
      $comment = $arr[$i]['comment'];
  }
}

?>
<div class='newMissionForm'>
<form method='POST' action='?p=editMissionUpdate' enctype="multipart/form-data">
<div class='masterHeading'>Oppdater oppdrag</div>
<input type='hidden' name='id' id='id' class='inputClass' value='<?php echo $id ?>'>
<div class='form1'><label for='date' class='labelClass'>Dato</label><input type='date' name='date' id='date' class='inputClass' value='<?php echo $date ?>'></div>
<div class='form1'><label for='mission' class='labelClass'>Type oppdrag</label>
  <select class='form_control inputClass' id='mission' name='mission'>
    <option value=''>Velg oppdragstype</option>
    <option value='Vakt hverdag'<?php if ($mission == "Vakt hverdag") echo " selected='selected'"; ?>>Vakt hverdag</option>
    <option value='Vakt helg'<?php if ($mission == "Vakt helg") echo " selected='selected'"; ?>>Vakt helg</option>
    <option value='Vakt helgedag'<?php if ($mission == "Vakt helgedag") echo " selected='selected'"; ?>>Vakt helgedag</option>
    <option value='Vakt hel uke'<?php if ($mission == "Vakt hel uke") echo " selected='selected'"; ?>>Vakt hel uke</option>
    <option value='Vakt firedagers uke'<?php if ($mission == "Vakt firedagers uke") echo " selected='selected'"; ?>>Vakt firedagers uke</option>
    <option value='Tillegg helgedag'<?php if ($mission == "Tillegg helgedag") echo " selected='selected'"; ?>>Tillegg helgedag</option>
  </select>
  <div id='missionInfo1' class='<?php if ($mission !== 'Vakt hverdag') { echo ' none'; } ?> missionInfo'><?php infoVaktHverdag() ?></div>
  <div id='missionInfo2' class='<?php if ($mission !== 'Vakt helg') { echo ' none'; } ?> missionInfo'><?php infoVaktHelg() ?></div>
  <div id='missionInfo3' class='<?php if ($mission !== 'Vakt helgedag') { echo ' none'; } ?> missionInfo'><?php infoVaktHelgedag() ?></div>
  <div id='missionInfo4' class='<?php if ($mission !== 'Vakt hel uke') { echo ' none'; } ?> missionInfo'><?php infoVaktUke() ?></div>
  <div id='missionInfo5' class='<?php if ($mission !== 'Vakt firedagers uke') { echo ' none'; } ?> missionInfo'><?php infoVakt4dgUke() ?></div>
  <div id='missionInfo6' class='<?php if ($mission !== 'Tillegg helgedag') { echo ' none'; } ?> missionInfo'><?php infoTilleggHelg() ?></div>
</div>
<div class='form1'><label for='from' class='labelClass'>Transport fra</label><input type='text' name='from' id='from' class='inputClass' value='<?php echo $from ?>'></div>
<div class='form1'><label for='to' class='labelClass'>Transport til</label><input type='text' name='to' id='to' class='inputClass' value='<?php echo $to ?>'></div>
<div class='form1'><label for='payment' class='labelClass'>Lønn</label><input type='text' name='payment' id='payment' class='inputClass readonly' value='<?php echo $payment ?>' readonly></div>
<div class='form1'><label for='comment' class='labelClass'>Kommentar</label>
  <textarea name='comment' id='comment' class='inputClass2'><?php echo $comment ?></textarea></div>

<button type="submit" name="submit_form" class="btn btn-primary">Oppdater oppdrag</button>
</form>
<?php btnCancel(); ?>
</div>

函数 getMIssionsID() :

public function getMissionsId()
 {
     $arr = array();
     $mission_id = isset($_GET['id']) ?  $_GET['id'] : '';
     $statement = $this->conn->prepare("SELECT id, username, date, mission, transpFrom, transpTo, payment, comment, created_at from missions where id = $mission_id");
     //echo $this->conn->error;
     $statement->bind_result($id, $username, $date, $mission, $from, $to, $payment, $comment, $created_at);
     $statement->execute();
     while ($statement->fetch()) {
       $arr[] = [ "id" => $id, "username" => $username, "date" => $date, "mission" => $mission, "transpFrom" => $from, "transpTo" => $to, "payment" => $payment,
       "comment" => $comment, "created_at" => $created_at];
     }
     $statement->close();

     return $arr;
 }

发出post命令时调用的文件（editmissionupdate.php）：

<?php
require_once("db.php");

 $id = intval($_POST['id']);
 $mission = strip_tags($_POST['mission']);
 $rawdate = htmlentities($_POST['date']);
 $date = date('Y-m-d', strtotime($rawdate));
 $from = strip_tags($_POST['from']);
 $to = strip_tags($_POST['to']);
 $payment = strip_tags($_POST['payment']);
 $comment = strip_tags($_POST['comment']);

 $conn->updateMission($id, $mission, $date, $from, $to, $payment, $comment);
?>

<div style='width: 50em'>
<div class='masterHeading'>Oppdraget er oppdatert</div>
  <br><br>
  <div class='descrText'>Oppdraget ble vellykket oppdatert.</div>
<?php btnCancel(); ?>
</div>

函数 updateMission() :

public function updateMission($id, $mission, $date, $from, $to, $payment, $comment)
 {
     $statement = $this->conn->prepare("UPDATE missions SET mission = ?,date = ?,transpFrom = ?,transpTo = ?,payment = ?,comment = ? WHERE id = ?");
     echo $this->conn->error;
     $statement->bind_param('ssssssi', $mission, $date, $from, $to, $payment, $comment, $id);
     $statement->execute();
     $statement->close();

 }